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Pictures of the Future
The Magazine for Research and Innovation

Power Transmission

Plug-and-Play Transformer Ensures Reliable Electricity

In the event of power outage the installation of a mobile transformer allows safe and reliable grid connection, restoring power within one day.

Siemens has built power transformers for extra-high-voltage (EHV) grids that can be installed within one week. Until now, this process has taken several weeks. In the event of an outage, the new transformers can restore power in a period of time that in the past would have seemed impossible.

Power transformers ensure the transmission of hundreds of kilovolts (kV) of electricity over long distances all the way to the end customer. If such a transformer fails in a large city, thousands of people can be affected. Ordering and delivering a new transformer has usually taken more than six months.

To ensure that power is not disrupted, electricity should be redirected to other parts of the grid instantly. The greater the level of redundancy built into a grid, the more resistant it will be to outages. That’s why many utility companies that serve major urban centers keep a backup transformer on hand. But it still takes several weeks to put a transformer of this power class into operation on site. Siemens’ mobile solution decreases this period to less than one week.

The Risk of Failure Increases with Age

Power transformers are designed to operate for decades. Indeed, they often remain in use beyond their guaranteed service life, even as the probability of an outage increases. Damaged lines, or other causes of grid failure such as natural disasters, can also result in outages. However, with the help of systems that continuously record a transformer’s status, it is possible to detect a pending outage in a timely manner. The problem is that many systems are not equipped with condition monitoring capability. In regions served by a relatively old power grid or regions that are subject to a high risk of extreme weather events, backup transformers can ensure extra reliability.

Until now, transformers with a capacity of several hundred megavolt-amperes (MVA) weighed up to several hundred tons and therefore required heavy-duty transport to reach an installation site. Such transformers are filled with mineral oil that can ignite in the event of a malfunction and pollute the environment if an uncontrolled discharge occurs (the transformers are not filled with mineral oil when shipped.) What’s more, they require a huge amount of labor-intensive precision work – usually about two to three weeks’ worth – before they can enter service.

Instead of mineral oil the transformer contains environment friendly ester oil, which can remain in the tank during shipment.

Plug-and-play Feature Shortens Connection Time by Several Weeks

In collaboration with several customers, Siemens has developed a mobile transformer for a voltage of 345 kV that can be put into operation within a time frame that previously would have seemed impossible. The innovation lies in the intelligent combination of several established technologies. The transformer is connected via leads to the power grid. In the past, the leads had to be connected inside the transformer to the windings, a process that took a large amount of time and effort. With the solution developed by Siemens, it is now possible to use plug-and-play leads at the 345-kV level. The new leads snap into place using plug connections, and as a result installation only takes one day.

Transportation is also easier. Most power transformers are designed to be three-phase units; in other words, they process all alternating currents that are transmitted over lines in three offset phases. The mobile solution consists of three much smaller single-phase transformers, which considerably simplifies transportation. In addition, the mobile system can be insulated with environment-friendly ester oil, which can remain in the tank during shipment so that the draining and refilling steps are no longer necessary. 

Siemens has already developed seven “plug-and-play” transformers for its customers. The systems transform 345 kV to 136 kV and 132 kV to 68 kV. Plug-and-play transformers can be used at various voltage levels.

Christine Rüth